It would be nice to be able to mark answers that are really useful reference material, i.e. that provide interesting information that is not readily available with google - probably in response to a "difficult" question.
And the UI could provide a way to view answers that have been marked in this way. Perhaps a minumum rep would be needed to do so: and to help stop gaming, moderators could vote for such marks to be removed like they currently vote for questions to be closed.
Marking answers as such does not necessarily need to give rep to the answerer - though possibly the increased visibility of such answers will make them attract more upvotes.
It would make the site more interesting - I would like to be able to choose a subject using tags, and browse what others consider to be interesting information - more fun than yet another question answer on the IDisposable pattern in .NET
Isn't that the purpose of votes?
Not at all. A cursory look at StackOverflow shows a poor correlation between number of votes and the usefulness of an answer as reference material. Votes are tied to rep so often gamed, and in any case, they are more related to how well the question was answered rather than how "interesting" it is.
You're walking into subjective territory here...
Definitely. Which is why probably some minimum rep ought to be needed to do this, why a moderator should be able to override it, and why it probably shouldn't attract any rep.
My point is I'd find it interesting to browse what other people I respect consider to be useful reference material. Perhaps another way to do this would be to allow users to mark answers as a "favorite" in the same way questions can be marked today. And we could then browse the answers that, say, Jon Skeet has marked as favorites. An answer may be useful by virtue of going beyond what was asked in the question, so that marking a question as a favorite is not necessarily appropriate.
What's really useful to a .net beginner might not be at all useful to a .net expert.
Absolutely. I would not expect answers to beginner questions to be marked in this way if the information is readily available (e.g. on MSDN for .NET stuff).